The amount that the average American drives each year has been declining for nearly a decade, yet most transportation agencies are still making decisions based on the notion that a new era of ceaseless traffic growth is right around the corner.

The Wisconsin Department of Transportation, for example, has overestimated traffic on its roads by an average of 73 percent, according to a recent study. And Dallas-area planners recently produced traffic projections that predicted a much larger increase in driving than the state DOT was even predicting.

That’s why a new traffic forecast from the Washington State Office of Fiscal Management is so interesting: It actually acknowledges how travel habits are changing. Seattle-based environmental think tank Sightline spotted the above traffic projection in a new government report. In its most recent financial forecast, the agency has abandoned the assumption of never-ending traffic growth that it employed as recently as last year. Instead, the agency has responded to recent trends, even projecting that total traffic will start to decline within the next ten years.

Sightline’s Clark Williams-Derry says that’s huge:

By undermining both the rationale for new roads and the belief that we’ll be able to pay for them, a forecast of flat traffic should help inject a needed dose of reality into the state’s transportation debates.

Of course, there’s no telling whether this forecast will be right. As Yogi Berra allegedly said, predictions are hard, especially about the future. But if it turns out that this forecast underestimates traffic growth, budgeters won’t find it such an unpleasant surprise, since more traffic will bring more revenue from drivers.

Update: This post has been amended to reflect that the traffic forecast was published by the Washington State Office of Financial Management, not the Washington State DOT, as originally reported. According to the OFM report, however, the projections were produced by a division of the DOT.